Bridge structure

ABSTRACT

A bridge supports any desired loading capacity to cross rivers, ravines, highways, wetlands, and other areas where traffic or pedestrians conveniently access the opposite side. The structure is assembled in a number of ways at the bridge site, using smaller equipment and less time than is normally required. The prefabricated and trial fitted elements can be assembled at ground level and the structure can be launched on rollers across the area that is to be crossed, or can be assembled sequentially from one or both sides. The structure includes two or more box trusses supporting the bridge deck which is integrated into the structure. The upper portion of the trusses form the side barriers of the bridge and the deck with integrated cross members is fastened to the lower portion of the trusses, both of which are sized to accommodate the load bearing capacity of the traffic using the structure.

RELATED APPLICATIONS

This application is based upon provisional application No. 60/995,548, filed Sep. 27, 2007, which application is incorporated by reference herein. Applicant claims benefit under 35 U.S.C. §119(e) therefrom.

FIELD OF THE INVENTION

The present invention relates to short to medium span bridges across highways and other crossing requirements such as rivers, railroads, ravines, and wetlands. As designed, these bridges are totally prefabricated in the factory and preassembled to the greatest extent possible to ensure the proper fit of all of the elements which make up the completed bridge structure. This is done to speed up the erection time and to minimize or eliminate any costly and time consuming field labor.

There are many types of prefabricated bridges available from various manufacturers today. Most of these are used as temporary structures which can be erected quickly to be used while a permanent bridge structure is built and then disassembled and removed from the site. This extra work and time consumed is both costly and an inconvenience to the users of the bridge structure. The truss designs of these temporary bridges are not particularly appealing and the loads they are capable of supporting are generally less than that which is required for a permanent bridge structure.

OBJECTS OF THE INVENTION

It is therefore an object of this invention to provide a prefabricated bridge structure which can support the heaviest traffic loads that are required.

It is another object of this invention to provide a prefabricated bridge structure which can be assembled at the bridge site quickly, with a minimum number of elements which have been previously assembled where manufactured and then disassembled and shipped to the permanent site for rapid assembly into the finished bridge structure.

It is a further object of this invention to provide a prefabricated bridge structure that will last for a long period of time without being affected by weather or temperature conditions and require a minimum of maintenance.

Yet another object of this invention is to limit the number of bolted members which are the primary cause of bridge failures due to the flexing of the attachment points of the members, when subjected to the varying and cyclical loading of these areas by the traffic moving across the structure.

It is also an object of this invention to design a bridge structure completely out of metal and other flexible materials which can yield and then return to their original position without cracking or becoming permanently deformed.

Still another object of this invention is to provide a structure that has no areas that are difficult to paint or maintain in order to limit the possibility of corrosion of the metal portions of the structure.

A further object of this invention is to protect the inaccessible interior areas of the bridge structure from corrosion by completely sealing those areas or filling them with foam to eliminate the entrance of oxygen in the air which is the primary cause of corrosion in these inaccessible metal areas.

An additional object of this invention is to provide a bridge structure in which all of the elements work together to give the finished structure the strength and rigidity to satisfy all of the conditions to which the bridge will be subjected.

Yet another object of this invention is to provide a bridge structure in which the bridge barriers work in composite with the deck and substructure to form the trusses necessary to support the imposed loads to which the bridge will be subjected.

There are many other objectives to which this invention can be applied such as erection and launching from one or both sides of the area that is to be crossed, combining bridge spans parallel to one another to provide additional lanes to create multiple lane two way traffic bridges, sequential launching of bridge segments from portions of the structure that have already been erected to build long causeways over swampy or shallow water areas where there might be difficulty in placing or supporting heavy construction equipment, and many others that are too numerous to mention.

SUMMARY OF THE INVENTION

The bridge of this invention includes trusses composed of upper and lower truss chords connected together by side plates and diaphragms to form a boxed truss with its upper portion shaped like a partially sloped highway barrier. Deck support beams are attached between the lower chords of the trusses to support the orthotropic deck panels, which are fastened to the top of the cross beams. The orthotropic deck panels form a bridge deck made of steel or aluminum plates supported by ribs, such as undulating arcuate ribs, underneath. The panels are also attached to the lower portion of the barrier shaped inner panels of the trusses. These orthotropic deck panels become the riding surface of the bridge and serve as a horizontal diaphragm to accommodate the horizontal forces to which the bridge will be subjected. The lower portion of the inner barrier panel can be made out of stainless steel to avoid corrosion in this area due to the scraping of the painted surface by snowplows and the wheels of vehicles which rub against these areas. From a practical point of view, this bridge design is best suited for two or three lane traffic. If more than two or three traffic lanes are required, a center divider truss can be made with both upper adjacent sides having the shape of a highway barrier. This enables the doubling of the width of the bridge and provide a separation for the traffic which is moving in opposite directions. The orthotropic panels have a temporary riding surface applied in the place where they are manufactured, which becomes the base on which the permanent macadam riding surface is applied in the field when all of the work is completed.

To summarize, the bridge is made of two side trusses made up of upper and lower chords, which have stiffeners and diaphragms welded between them. Plate metal skins are fastened to the trusses to form a box truss, the upper portion of which is in the shape of a highway barrier having sloped lower mid portion, forming a trapezoid when viewed in cross section, attached to a vertical upper portion, forming a rectangle when viewed in cross section. The metal may be steel, carbon steel, aluminum or other suitable materials. Cross beams are attached to web stiffeners which are fastened between the flanges and web of the lower truss chords and protrude through the inside cover plate of the lower chord to provide a connection point for the cross beams. Orthotropic deck panels are placed on top of these cross beams and fastened to the cross beams and to an angle which is welded to the upper portion of the lower inside truss chord cover panel and to each other to create a continuous horizontal diaphragm which is also connected to the truss.

The structure thus created essentially becomes a horizontal beam with the trusses acting as flanges and the deck acting as the web. The trusses, which are connected together by the orthotropic deck, have the weight carrying capacity to accommodate the vehicular traffic that will be traveling across the bridge.

In the case where longer spans are required, which requires deeper side trusses, reinforced openings can be cut into the web of the upper truss top chord and the inner and outer skins above the level of the highway barrier to create a less confining atmosphere for the drivers and occupants of the vehicles using the bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can best be understood in conjunction with the accompanying drawings. It should be noted that the invention is not limited to the precise embodiments shown on the drawings, in which:

FIG. 1 is a cross sectional schematic of the invention illustrating the various elements in their combined form which make up the structure of the bridge. The sizes of the elements may vary from one structure to another to enable the engineer or designer of the bridge to adapt or combine these elements to suit the requirements for the structure, such as length, width, load bearing capacity, and other factors that have to be considered to accomplish the desired bridge design.

FIG. 2 is a longitudinal section of a portion of the bridge illustrating the various elements in the combined form which make up the structure of the bridge.

FIG. 3, shown in the circular detail viewing circle of FIG. 1, is a detail of the stainless steel edge guard which is attached to the lower edge of the inside face of the lower sloped barrier portion of the side girder where it connects to the deck plate and to the continuous deck support angles, also known as projecting corners.

FIG. 4, shown in the detail viewing ellipse of FIG. 1, is a detail of the upper portion of the removable inside access face plate which is attached to a vertically extending tapped bar welded to the top edge of the upper chord of the side box girder of the bridge and to tapped bars welded to the two adjacent box girder diaphragms at the place where a splice of the bridge sections is desired.

FIG. 5, shown in the detail viewing ellipse of FIG. 2, is a detail of the attachment of the diaphragm or web stiffener edge bars to the inside girder face plates by plug welding the protruding edge bar of the diaphragm or web stiffener through slots cut into the inside girder face plates.

FIG. 6, shown in the detail viewing ellipse of FIG. 2, is an alternate detail to the bolted connected means of FIG. 5 for attaching the edge of the diaphragms to the inside face cover plate of the side box girders, by welding a tapped bar onto the edge of the diaphragm or web stiffener and fastening both members together with appropriate sized fasteners.

FIG. 6A is a detail cross sectional view of a detail of FIG. 6.

FIG. 6B is an isometric view of the a portion of the upper cover plate.

FIG. 7, shown in the detail viewing ellipse of FIG. 2, is a cross sectional view of the connection between the cross beams/floor beams and the protruding web stiffeners, using angles which have holes matching those in the lower beam web stiffener extensions and which are bolted to the lower beam cover plate, thus forming knife connections for the attachment of floor beams and the diaphragms of the deck plate assemblies.

FIG. 8, shown in the detail viewing circle of FIG. 1, is a front cross sectional view of the cover plate connection for the opening needed to access the lower chords of the side box trusses to facilitate the splice plate bolting of the lower beams together needed to assemble the bridge.

FIG. 8A is a cross sectional view of the cover plate with the tapped edge bar of the detail view of FIG. 8.

FIG. 9, shown in the detail viewing ellipse of FIG. 11, is an isometric view of the assembly of the elements and the method of connecting two of the box girder sections together before the cover plate shown in FIG. 6 is secured in place.

FIG. 9A is a cross sectional view of the assembly of FIG. 9.

FIG. 10, shown in the detail viewing ellipse of FIG. 1, is a cross sectional view of the orthotropic deck panel and its attachment to the crossbeam.

FIG. 11 is an isometric view of an assembled bridge section with a schematic view of the elements used to connect two bridge sections together.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section of the invention with the details of the position of the elements that make up the bridge structure of the invention. For example, FIG. 1 shows the bridge structure of this invention which includes trusses composed of an upper truss chord having an upper chord beam 2 and a lower truss chord having a lower chord beam 1, connected together by outer side plate 3 and inner side plate 4 and diaphragms 11 to form a boxed truss with its upper portion shaped like a partially sloped highway barrier having an upper part shaped like a rectangle in cross section attached to a lower sloping part shaped like a trapezoid in cross section. Deck support beams are attached between the lower chords of the trusses to support the orthotropic deck panels, which are fastened to the top of the cross beams. The orthotropic deck panels form a bridge deck made of steel or aluminum plates 9 supported by deck support ribs 13 underneath. The panels are also attached to the inner lower chord cover plates 5 of the lower portion of the barrier shaped inner panels of the trusses. These orthotropic deck panels formed by plates 9 and ribs 13 become the riding surface of the bridge and serve as a horizontal diaphragm to accommodate the horizontal forces to which the bridge will be subjected. The lower portion of the inner barrier panel, such as, for example, projecting corner angle members 6, can be made out of stainless steel to avoid corrosion in this area due to the scraping of the painted surface by snowplows and the wheels of vehicles which rub against these areas.

FIG. 2 is a longitudinal view of the invention with the position of the diaphragms 11 and web stiffeners 8, as well as in FIG. 7 (in the detail ellipse labeled FIG. 7 of FIG. 2), showing the bolting 18 to the cross beams 16 and the deck cross beam diaphragm 10.

FIG. 3 is a detail of the stainless steel snow plow paint protection corner angle 6 and its connection to the horizontal deck plate 9, the inside lower chord cover plate 5, the deck support corner angle 12, and the inside face plate 4 of the box girder with the stainless steel corner angle 6.

FIG. 4 is a detail of the connection of the partially sloping inner box truss cover plate 26 having a distal projecting retaining lug with a grasping tab portion reaching over and attached to an upper distal end of the outer truss backplate 3 and the tapped bar 14, which is welded to the edge of the horizontally extending top flange of the upper chord beam 2 of the upper chord of the truss 2, or shop welded directly to the backplate 3.

FIG. 5 is a detail of one method of securing the inner cover plate 4 to the diaphragms 11 via slots 19 cut into the cover plate 4 at the diaphragm 11 locations and plug welding the diaphragm to the cover plate 4 through the slots 19.

FIG. 6 shows a method of securing the diaphragms to the inside girder access cover plate 26 by welding a tapped bar onto the edge of the diaphragm which is to be used to attach the diaphragm to the inside girder access cover plate 26, through matching holes drilled into the cover plate 26.

FIG. 6A is a detail cross sectional view of a detail of FIG. 6.

FIG. 6B is an isometric view of a portion of the upper cover plate 26.

FIG. 7 is a detail of the protruding web stiffener extension plates 20 that connect the cross beam 16 and the deck panel diaphragm 10 to the side box truss shown in FIG. 9 and to the knife connection corner angle 17. It also illustrates the sloped epoxy concrete region 25 or other suitable material that is placed on top of the crossbeam flanges, which prevents birds from standing or nesting in those areas and greatly reduces the incidence of corrosion that their excrement is responsible for.

FIG. 8 is a detail of the cover plate 23 with the tapped edge bar 24 welded to its periphery 23 that covers the opening 22 for the access required for bolting the lower chord beam 1 and splice plates 7 shown in FIGS. 1 and 9.

FIG. 8A is a cross sectional view of the cover plate 23 with the tapped edge bar 24 of the detail view of FIG. 8.

FIG. 9 is an isometric view of the assembly of FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8.

FIG. 9A is a cross sectional view of the assembly of FIG. 9.

FIG. 10 is a cross sectional view of the orthotropic deck panel attached to the cross beam 16 and to the box truss corner angle 17 and to the lower web stiffener extensions 20 of FIG. 9. The crossbeam 16 and deck diaphragms 10 with appropriate fasteners 18 are used to complete this assembly.

FIG. 11 is a combined perspective view of all of the FIGS. 1 through 10, illustrating the referenced bridge and the manner in which they are assembled to produce the desired structure, with a cutaway view of the side box truss elements showing the arrangement of these interior elements and the orthotropic deck plate 9 with the attached ribs 13 and diaphragm 10.

In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiment. However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention.

It is further known that other modifications may be made to the present invention, without departing the scope of the invention, as noted in the appended Claims.

NUMERICAL LIST OF THE ELEMENTS OF THE INVENTION

-   1. Lower chord beam -   2. Upper chord beam -   3. Outer back plate of side girder -   4. Inner girder cover plate -   5. Inner lower chord cover plate -   6. Stainless steel snowplow protection angle -   7. Upper and lower chord splice plates -   8. Web stiffener plates -   9. Bridge orthotropic deck plate -   10. Orthotropic deck crossbeam diaphragm -   11. Box girder diaphragms -   12. Orthotropic deck support angle -   13. Orthotropic deck support ribs -   14. ¾″ thick tapped bar -   15. Holes for fasteners -   16. Crossbeams -   17. Crossbeam knife connection angles -   18. Appropriate connection fasteners -   19. Detail of plug weld in slot -   20. Lower chord web stiffener extension plate -   21. Tapped bar welded to inside edge of diaphragm -   22. Splice plate access bolting opening -   23. Splice plate bolting opening cover plate -   24. Tapped edge bar of cover plate -   25. Sloped cement-like material with anchors to exposed flanges -   26. Upper inner box girder access cover plate -   27. Plug weld backup bar -   28. Textured riding surface -   29. Internal tapped splice plate welded to upper and lower chord     beam webs 

1. A bridge being an assembly of structural elements, acting together to provide a structure of the high strength and durability which is required to meet the great load carrying capacity and long service life that can be anticipated for this type of structure; said bridge assembly comprising:. at least one box truss composed of a pair of left and right side box girders, each having respective upper and lower truss chords connected together by side plates and diaphragms to form a boxed truss with a respective upper portion shaped like a partially sloped highway barrier; each said box girder forming a barrier structure; deck support beams being attached between said lower chords of said at least one truss supporting a respective orthotropic deck panel, said orthotropic deck panel being fastened to respective tops of said cross beams, said orthotropic deck panel forming a bridge deck made of at least one surface plate supported by longitudinal ribs underneath; said orthotropic deck panel being attached to respective lower portions of said barrier shaped inner panels of said at least one box truss, said orthotropic deck panels becoming a riding surface of the bridge and serving as a horizontal diaphragm accommodating the horizontal forces to which the bridge is subjected.
 2. The said bridge as in claim 1 wherein respective supporting composite box girders/barrier structure of said box truss also act to form the side barriers to protect vehicles and pedestrians from falling off the side of the bridge structure.
 3. A bridge structure as in claim 2 wherein the bridge side barriers form the upper portion of said box truss that supports said bridge deck surface.
 4. A bridge structure as in claim 3 in which said bridge deck surface plate is attached to the side of said composite box girder/barrier structure to eliminate the lateral movement of the side box girder/barrier structure.
 5. A bridge structure as in claim 4 in which said bridge deck surface plate and said supporting longitudinal ribs have a transverse diaphragm attached to respective extensions of respective lower side beam web stiffeners protruding through respective slots in respective lower inner side beam cover plates of said box truss, by bolting through respective matching holes.
 6. A bridge structure as in claim 5 in which a respective transverse diaphragm of said bridge deck surface plate is attachable to a beam attached to a respective extension of said lower portion of said side beam web stiffeners and to a respective diaphragm, to create a much longer and deeper transverse beam capable of carrying the weight of additional deck plate assemblies, in order to provide for additional lanes of vehicular traffic using said bridge.
 7. A bridge structure as in claim 2 in which said side box girder assemblies are made of shorter segments, and field bolted together with the aid of splice plates, to make transportation and field assembly simpler.
 8. A bridge structure as in claim 3 in which said splice plates can be accessed for bolting via openings in a surface of said box girder, and in which the openings can be closed with respective bolted cover plates.
 9. A bridge structure as in claim 8 in which respective inner girder elements can be accessed more easily by making a portion of respective upper inside cover plates 4 of said box truss assembly removable to create the access necessary for the joining of respective shorter segments of said side box girder assemblies into lengths required for a span of said bridge.
 10. A bridge structure as in claim 4 in which said bridge deck surface plate is supported by and bolted to an angle attached to said inner cover plate of said lower beam of said supporting box girder and to said lower chord web stiffener extension, thus forming a knife connection for greater strength at this point.
 11. A bridge structure as in claim 10 in which said angle formed by said bridge deck surface plate and said upper inner cover plate is covered by a stainless steel angle which reinforces this area formed by said bridge deck surface plate and said upper inner cover plate and limits the corrosion that occurs when snow plows and other equipment scrape the paint from metal that would normally be used in this area.
 12. A bridge structure as in claim 5 onto which epoxy concrete is placed to form a slope on all protruding flanges and horizontal surfaces of the underside of said bridge structure to eliminate areas on which birds can nest and congregate, to eliminate the corrosion caused by bird excrement.
 13. A bridge structure as in claim 9 which has an inside splice cover panel with holes to provide access for bolting respective splices of said upper and lower chord beams of said side box girder.
 14. A bridge structure as in claim 1 on which a textured riding surface is applied to said bridge deck surfaces to prevent skidding of vehicles using the bridge.
 15. A bridge as in claim 3 in which said side barriers of said side box girders include said upper chord beam, said inner girder cover plate, said outer back plate, and said diaphragms between said upper chord beam and said lower chord beam.
 16. A bridge as in claim 2 in which said inner girder cover plate of said composite box girder is attached to respective diaphragms of said side box girders by plug welding a backup bar of respective diaphragms into matching slots cut into a respective face of said inner girder cover plates or by bolting to a tapped bar welded to an edge of said diaphragm through matching holes drilled into a respective face of said inner girder cover plate.
 17. A bridge as in claim 6 in which a connection angle with holes matching those in a lower chord beam web stiffener extension is bolted to said inner lower chord face plate to create a knife connection for said cross beam and a respective orthotropic deck crossbeam diaphragm.
 18. A bridge structure as in claim 1 in which a bridge girder is combined with a safety barrier structure to crate a bridge element of greater load bearing capacity without increasing the depth of said bridge girder, and to provide for the means to which said bridge roadway surface and its respective support structure can be connected.
 19. A method of assembling quickly a permanent bridge at a crossing site comprising the steps of: prefabricating a plurality of box trusses in which each truss has lengthwise front and rear ends, left and right sides, and comprises upper and lower truss chord beams connected together by an inner side plate on each of said left and right sides of said truss forming side walls of said truss, a horizontal deck panel extending between said side walls adjacent top edges of said lower truss chords, said side walls extending above said horizontal deck panel forming a highway barrier, and said horizontal deck panel having a temporary driving surface; factory assembling said box trusses by joining front and rear ends in a row of said box trusses to adjacent box trusses to form a bridge structure in an off site location to ensure proper fit of all elements which make up a completed bridge structure, thereby speeding up erection time at said crossing site; disassembling said bridge structure; transporting said box trusses to said crossing site; reassembling said box trusses at said crossing site to form said permanent bridge; and adding a permanent driving surface to said temporary driving surface on said horizontal deck panel, whereby said horizontal deck panel is an integral part of each box truss and serves as a horizontal diaphragm to accommodate horizontal forces to which said bridge will be subjected.
 20. The method of claim 19 in which the upper chord beam is made narrower in width than the lower chord beam in each truss whereby inner sides of said side walls slope outwardly from and above said horizontal deck panel.
 21. The method of claim 20 in which each upper chord beam is provided with an inner girder cover plate extending from said inner side plate to and overlapping a top of said upper chord beam, joining an outer back plate forming a smooth upper wall surface of each of said side walls.
 22. The method of claim 21 in which two rows of trusses are arranged side by side whereby adjacent side walls of side by side trusses form a road median or divider.
 23. A box truss for use in bridge construction comprising: said truss having lengthwise front and rear ends, left and right sides, and comprises upper and lower truss chord beams connected together by an inner side plate on each of said left and right sides of said truss forming side walls of said truss, a horizontal deck panel extending between said side walls adjacent top edges of said lower truss chords, said side walls extending above said horizontal deck panel forming a roadway barrier, and said horizontal deck panel having a paved surface; longitudinally extending ribs mounted on an underside of said horizontal deck panel for providing rigidity and support for said horizontal deck panel; said upper and lower chord beams having inner cover plates; and an outer back plate extending from a top of said upper chord beam to a bottom of said lower chord beam on each side of said truss giving a smooth side surface of said truss.
 24. The box truss of claim 23 in which said upper chord beam is narrower in width than said lower chord beam whereby inner sides of said side walls slope outwardly above said horizontal deck panel.
 25. The box truss of claim 24 in which each upper chord beam has an inner girder cover plate extending from said inner side plate to and overlapping a top of said upper chord beam, joining an outer back plate forming a smooth upper wall surface of each of said side walls.
 26. The box truss of claim 25 further comprising a weather resistant angled corner located at a corner region where said horizontal deck panel and each said side of said box truss.
 27. A bridge comprising: a plurality of trusses, each truss having lengthwise front and rear ends, left and right sides, and comprising upper and lower truss chord beams connected together by an inner side plate on each of said left and right sides of said truss forming side walls of said truss, a horizontal deck panel extending between said side walls adjacent top edges of said lower truss chords, said side walls extending above said horizontal deck panel forming a roadway barrier, and said horizontal deck panel having a paved surface for driving or walking; longitudinally extending ribs mounted on an underside of each said horizontal deck panel for providing rigidity and support; said upper and lower chord beams having inner cover plates; an outer back plate extending from a top of said upper chord beam to a bottom of said lower chord beam on each side of said truss giving a smooth outer side surface of said truss; and said trusses joined in a row of front and rear to adjacent trusses to form said bridge, providing a continuous pavement on adjoining horizontal deck panels.
 28. The bridge of claim 27 in which the upper chord beam is narrower in width than the lower chord beam in each truss whereby inner sides of said side walls slope outwardly from and above said horizontal deck panel.
 29. The bridge of claim 28 in which each upper chord beam has an inner girder cover plate extending from said inner side plate to and overlapping a top of said upper chord beam, joining an outer back plate forming a smooth upper wall surface of each of said side walls.
 30. The bridge of claim 29 in which two rows of trusses are arranged side by side whereby adjacent side walls of side by side trusses form a road median or divider.
 31. The bridge of claim 27 further comprising a weather resistant angled corner located at a corner region where said horizontal deck panel and each said side of said box truss.
 32. A bridge comprising at least one truss composed of upper and lower truss chords connected together by side plates and diaphragms to form a boxed truss with a respective upper portion shaped like a partially sloped highway barrier; deck support beams being attached between said lower chords of said at least one truss supporting a respective orthotropic deck panels, said orthotropic deck panel being fastened to respective tops of said cross beams, said orthotropic deck panel forming a bridge deck made of metal plates supported by ribs underneath; said panels being attached to respective lower portions of said barrier shaped inner panels of said at least one truss, said orthotropic deck panels becoming a riding surface of the bridge and serving as a horizontal diaphragm accommodating the horizontal forces to which the bridge is subjected.
 33. The bridge as in claim 32 wherein a lower portion of said inner barrier panel is weather resistant stainless steel.
 34. The bridge assembly as in claim 1, wherein said bridge assembly comprises metal.
 35. The bridge assembly as in claim 1 wherein the metal is selected from the group consisting of steel, carbon steel, or aluminum.
 36. The bridge as in claim 11 wherein the metal is selected from the group consisting of steel, carbon steel, or aluminum.
 37. The bridge as in claim 32 wherein the metal is selected from the group consisting of steel, carbon steel, or aluminum. 